MATING-TYPE CONTROL OF SEXUAL DEVELOPMENT IN COPRINUS-CINEREUS

The multiallelic mating type genes of the hymenomycete fungus Coprinus cinereus determine mating compatibility by regulating a developmental sequence that converts an asexual monokaryon into a fertile dikaryon. The genes map to two loci, A and B, and mating compatibility requires different alleles of genes at both loci. The A genes encode two classes of proteins with conserved but dissimilar homeodomain DNA binding motifs (HD1 and HD2), which identify their role in development a's transcriptional regulators. Transformation studies with cloned genes suggest that a compatible mating is sensed by combinatorial interactions between an HD1 and HD2 protein and that the N-terminal regions of these proteins are implicated in the specificity of this interaction. The B genes of C. cinereus have been cloned but their function is, as yet, unknown. In another species, Schizophyllum commune, the B genes encode pheromones and pheromone receptors. Although a pheromone response pathway is not apparent in cell, fusion in hymenomycetes, it now seems likely to be involved in maintenance of dikaryotic growth.